Three Weeks Ago, an Engineer Named Calvin French-Owen Resigned from OpenAI. Here's What He Learned.
July 15, 2025
Three weeks ago, Calvin French-Owen, a former Segment co-founder and seasoned engineer, quietly stepped away from OpenAI—a company at the center of the generative AI revolution. In a recent blog post, he offered a rare inside look into what it’s like to build some of the most advanced AI tools in the world, including Codex, OpenAI’s coding assistant and competitor to tools like Cursor and Claude Code.
French-Owen didn’t leave because of “drama,” he clarified. After helping build Codex from scratch in just seven weeks, he felt the itch to return to startup life. But before doing so, he shared a candid reflection on the chaotic, brilliant, and at times fragile inner workings of one of the fastest-growing tech companies in history.
From 1,000 to 3,000: Growth at Breakneck Speed
OpenAI tripled in size during French-Owen’s one-year stint—from 1,000 to 3,000 employees. That kind of expansion inevitably brings growing pains.
“Everything breaks when you scale that quickly: how to communicate as a company, the reporting structures, how to ship product, how to manage and organize people, the hiring processes…”
And yet, amid the chaos, the company still feels like a startup. Engineers are empowered to run with ideas without layers of red tape. But that also means duplicated efforts—French-Owen recalls seeing multiple internal libraries for things like queue management or agent loops. The coding talent is mixed: ex-Google veterans sit next to newly minted PhDs. The shared backend? “A bit of a dumping ground.”
Still, the company is aware of its technical debt and is actively trying to clean it up.
Building Codex on No Sleep
One of French-Owen’s standout memories was the creation of Codex. His team of about 17—engineers, researchers, designers, product leads—built the initial version in just seven weeks, working almost around the clock. The payoff was immediate.
“I’ve never seen a product get so much immediate uptake just from appearing in a left-hand sidebar, but that’s the power of ChatGPT.”
Launching Codex was one of those lightning-in-a-bottle moments that engineers and product teams dream about.
A Slack Company in a Giant’s Body
Despite its size and global influence, OpenAI still feels like a startup in many ways—yes, even running almost entirely on Slack. The vibe, French-Owen says, is reminiscent of early Facebook, with a “move fast and break things” energy. Many of the hires, in fact, come from Meta.
But it’s not all fast-moving product magic. The pressure is immense. With hundreds of millions of users and scrutiny from governments, competitors, and the public, OpenAI operates under a microscope. That has created a culture of secrecy, in part to avoid leaks and manage external narratives. Still, the team is keenly aware of what’s happening online.
“A friend of mine joked, ‘this company runs on Twitter vibes,’” French-Owen noted.
On AI Safety: Less Doom, More Practical Risk
Perhaps most striking is what French-Owen shared about the internal conversations on AI safety. Contrary to the common narrative that OpenAI ignores long-term AI risk, he paints a more nuanced picture.
The real focus, he says, is on immediate, practical threats: hate speech, abuse, bias manipulation, bio-weapon instructions, prompt injection, self-harm. While there are researchers at OpenAI thinking about long-term risks, the team is acutely focused on the fact that LLMs are already in widespread use—from therapy and coding to medical guidance and education.
In other words: safety isn’t theoretical anymore. It’s operational.
So Why Did He Leave?
Despite the high stakes, breakneck pace, and rocket-fueled product launches, French-Owen didn’t leave OpenAI because of burnout or frustration. He left because he wants to build again.
As a co-founder of Segment—acquired by Twilio for $3.2 billion in 2020—he’s no stranger to startup chaos. And now, after a year at OpenAI, he’s ready to return to the founder’s seat, bringing with him deep insights into what it takes to build—and scale—world-changing technology.
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